1. Technical Field
The present invention relates in general to an improved disk drive subassembly technique and, in particular, to an improved system, method, and apparatus for disk drive actuator pivot set height tooling with active servo compensation.
2. Description of the Related Art
Data access and storage systems generally comprise one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, one to five disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand rpm. Hard disk drives have several different typical standard sizes or formats, including server, desktop, mobile, and microdrive.
A typical HDD is shown in FIG. 1. An information storage system, such as a magnetic hard disk file or drive 111 for a computer system, has an outer housing or base 113 containing at least one magnetic disk 115. Disk 115 is rotated by a spindle motor assembly having a central drive hub 117. An actuator 121 comprises a plurality of parallel actuator arms 125 (one shown) in the form of a comb that is pivotally mounted to base 113 about a pivot assembly 123. A controller 119 is also mounted to base 113 for selectively moving the comb of arms 125 relative to disk 115.
Each arm 125 has extending from it at least one cantilevered load beam and suspension 127. A magnetic read/write transducer or head is mounted on a slider 129 and secured to a flexure that is flexibly mounted to each suspension 127. The read/write heads magnetically read data from and/or magnetically write data to disk 115. The level of integration called the head gimbal assembly is head and the slider 129, which are mounted on suspension 127. The slider 129 is usually bonded to the end of suspension 127. The head is typically pico size and formed from ceramic or intermetallic materials. The head also may be femto size and is pre-loaded against the surface of disk 115 by suspension 127.
Suspensions 127 have a spring-like quality which biases or urges the air bearing surface of the slider 129 against the disk 115 to enable the creation of the air bearing film between the slider 129 and disk surface. A voice coil 133 housed within a conventional voice coil motor magnet assembly 134 is also mounted to arms 125 opposite the head gimbal assemblies. Movement of the actuator 121 (indicated by arrow 135) by controller 119 moves the head gimbal assemblies radially across tracks on the disk 115 until the heads settle on their respective target tracks. The head gimbal assemblies operate in a conventional manner and always move in unison with one another, unless drive 111 uses multiple independent actuators (not shown) wherein the arms can move independently of one another.
Currently, the installation of pivot assemblies in the block of the actuator is limited by the achievable machining tolerances of each component (e.g., the actuator and pivot cartridge assembly). Unfortunately, the stack-up tolerance increases with respect to the z-axis (i.e., the axis of the pivot and actuator) to pivot mounting surface which, in high density hard disk drives, drives much of the head instability seen in current disk drives. This would improve current efforts on arm-to-disk height measurements which has been linked to screening head instable drives.
Prior art solutions include shims of thin metal or plastic that are used to offset parts via the thicknesses of the shims. Shims have limitations in that the addition of more parts to solve tolerances only can minimize the tolerance incurred, but not eliminate it since it, too, is a fixed height. Adjusting tooling to compensate for trends based on basic measurements can only average out the tolerance on a population of parts. However, adjusting tooling cannot eliminate or actively customize each mating part since it is static and not dynamic as in the case of the present invention. As will be described for the present invention, an adjustable or dynamic set height is required to improve the yield loss due to instable heads, as well as reduce overall cost losses from both internal manufacturing processes and incoming supplier parts. Thus, an improved solution for adjusting the set height for actuator pivots would be desirable.